In one of many articles covering the topic, Simon Aughton of PC Pro writes...

Facebook decided not to provide a mechanism for users to delete accounts themselves, but says that it is keeping the situation under review.

"We are measuring the effects of the change we made yesterday, and if we think more needs to be done to improve the user experience for deleting an account, we'll test different implementations and measure them accordingly," says Katie Geminder, director for user experience and design at Facebook.

Geminder explains that many users who deactivate their accounts later return to the site, so it is in their interest to retain their Facebook data. "On any given day, the number of users reactivating their accounts is roughly half of the number of users deactivating their accounts," she claims.